HF amplifier with switchable gain

ABSTRACT

A device for amplifying or attenuating HF signals is characterized in that a transistor is connected in a common-emitter configuration in amplifying operation, and a base-collector diode is connected in the forward-biased direction for attenuating operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No. PCT/EP03/04077 filed on Apr. 17, 2003.

BACKGROUND OF THE INVENTION

The invention concerns high-frequency amplifiers, and more particularly a radio-frequency amplifier which constitutes the input stage of a radio transmission system.

Since the signal levels in radio communication devices are subject to fluctuations of considerable magnitude (several tens of dB), it is necessary to adjust the stages following the input amplifier. Especially in the case of portable radio communication devices (e.g. mobile telephones), requirements concerning cost minimization and miniaturization are also important. This demands a simple circuit implementation. In order to accommodate this simple circuit implementation, a reduction in gain by a fixed amount suffices for certain applications. However, it is necessary in this context to ensure that the linearity of the amplifier does not change significantly, especially in the case of high input levels when the overall gain is to be reduced.

Known amplifiers with gain control either work with switchable passive attenuating elements or use electronically controlled attenuating elements (e.g. PIN diodes). In these three-layer diodes, the HF resistance can be controlled by means of a DC current in the forward direction.

SUMMARY OF THE INVENTION

The object of the present invention is to permit the necessary adjustment in gain inexpensively by means of a simple circuit implementation.

This is accomplished by a method and a device for amplifying or attenuating HF signals as a function of a DC configuration of a bipolar transistor. The transistor is operated in a common-emitter configuration in the amplifying operation. The base-collector diode is operated in the forward bias direction in an attenuating operation. A NPN bipolar transistor or a PNP bipolar transistor is employed. The HF signals contain a band of HF signals. A bipolar or a unipolar DC supply is employed. The operating states are switched by means of switching transistors or switching diodes. The base-emitter diode is unbiased or is connected in the blocking direction in an attenuating operation. The circuit arrangement may be asymmetrical or symmetrical. A variable resistor sets the current through the base-collector diode.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail with reference to the attached drawings, where:

FIG. 1 shows a circuit diagram of a circuit arrangement of the present invention,

FIG. 2 shows an equivalent circuit diagram to FIG. 1 for attenuating operation,

FIG. 3 shows a circuit diagram of another exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the invention, a circuit arrangement is created which uses the provision of DC voltages to permit switchable gain or attenuation of an HF signal. The circuit arrangement contains a bipolar transistor as an HF active element for both operating states. The transistor is wired in a common-emitter configuration. A distinction can be made between the two possible operating states; reference is made to FIG. 1 for the purpose of explanation. The matching elements needed in HF amplification for a good input/output reflection coefficient, maximum gain, and minimum noise amplification are known to the practitioner of the art, so they have been omitted from the figures for reasons of clarity.

Only the DC supply for the transistor is required to illustrate the inventive concept. In addition to the transistor, the diodes are also shown in order to indicate the polarity of the respective internal transistor diodes. The transistor is embodied in a conventional manner in a normal grounded-emitter circuit. In this exemplary embodiment with positive supply voltage, it is an NPN transistor; the opposite polarity with a PNP transistor would also be possible with a negative supply voltage. For amplifying operation 1, the connection 9 is connected to the positive supply voltage +Vcc and the impedance R3 is low-resistance; in contrast, for attenuating operation 2, the connection 9 is grounded and the impedance R3 is high-resistance. In the first case, the base voltage divider ensures that the base-emitter diode is operated in the forward-biased direction, and at this established operating point the transistor amplifies HF signals present at the base by way of the DC decoupling capacitor. The collector is connected to Vcc through an inductor L1 so as to be able to couple the amplified HF signal out through C2.

To operate the amplifier as an attenuating element, the base-collector diode is wired in the forward-biased direction, for example by connecting the collector branch to ground. In this configuration, only the base-collector diode is active and wired in the forward-biased direction. It acts as an HF attenuating element as a function of the current, set by R1, which flows through the diode. FIG. 2 shows the equivalent circuit resulting from this DC configuration.

FIG. 3 shows an additional exemplary embodiment. In this case, the switchover is accomplished by reversing the polarity of the supply voltage. To switch the states required for this operation, two diodes (D1, D2) are used. The HF characteristics of the circuit are achieved by the reversal of the operating voltage of the transistor. In amplifying operation 1, D1 conducts and D2 blocks. In this way, the transistor is provided with an appropriate bias voltage by the voltage divider R1, R2 and a collector current is set. In attenuating operation 2, D1 blocks and D2 conducts. In this case, the bias voltage is connected such that the base-collector diode conducts and acts as an HF resistance. Only the transistor is the HF active component in this circuit. The diodes perform only the DC switchover. Further exemplary embodiments, for example using switching transistors, are conceivable and to be viewed as variants. Moreover, the circuit arrangement can also be implemented symmetrically, for example using two transistors. 

1. Method of amplifying or attenuating HF signals as a function of a DC configuration of an NPN bipolar transistor, wherein the transistor is operated in a common-emitter configuration in amplifying operation, and the base-collector diode is operated in the forward-biased direction in attenuating operation.
 2. Method according to claim 1, characterized in that the HF signals contain a band of HF signals.
 3. Method according to claim 1, further comprising a bipolar DC supply.
 4. Method according to claim 1, further comprising a unipolar DC supply.
 5. Method according to claim 1, characterized in that the operating states are switched by means of switching transistors.
 6. Method according to claim 1, characterized in that the operating states are switched by means of switching diodes.
 7. Method according to claim 1, characterized in that the base-emitter diode is unbiased.
 8. Method according to claim 1, characterized in that the base-emitter diode is connected in the blocking direction in attenuating operation.
 9. Method according to claim 1, characterized in that the bipolar transistor is connected in an asymmetrical circuit.
 10. Method according to claim 1, characterized in that the bipolar transistor is connected in a symmetrical circuit.
 11. Method according to claim 1, characterized in that a variable resistor sets the current through the base-collector diode.
 12. Method of amplifying or attenuating HF signals as a function of a DC configuration of an PNP bipolar transistor, wherein the transistor is operated in a common-emitter configuration in amplifying operation, and the base-collector diode is operated in the forward-biased direction in attenuating operation.
 13. Circuit arrangement for amplifying or attenuating HF signals as a function of a DC configuration of an NPN bipolar transistor, wherein the transistor is in a common-emitter configuration for amplifying operation, and the base-collector diode is in the forward-biased direction for attenuating operation.
 14. Circuit arrangement according to claim 13, characterized in that the HF signals contain a band of HF signals.
 15. Circuit arrangement according to claim 13, further comprising a bipolar DC supply.
 16. Circuit arrangement according to claim 13, further comprising a unipolar DC supply.
 17. Circuit arrangement according to claim 13, characterized by switching transistors for switching the operating states.
 18. Circuit arrangement according to claim 13, characterized by switching diodes for switching the operating states.
 19. Circuit arrangement according to claim 13, characterized in that the base-emitter diode is unbiased.
 20. Circuit arrangement according to claim 13, characterized in that the base-emitter diode is connected in the blocking direction in attenuating operation.
 21. Circuit arrangement according to claim 13, characterized in that the circuit arrangement is asymmetrical.
 22. Circuit arrangement according to claim 13, characterized in that the circuit arrangement is symmetrical.
 23. Circuit arrangement according to claim 9, characterized in that a variable the resistor sets the current through the base-collector diode.
 24. Circuit arrangement for amplifying or attenuating HF signals as a function of a DC configuration of an PNP bipolar transistor, wherein the transistor is in a common-emitter configuration for amplifying operation, and the base-collector diode is in the forward-biased direction for attenuating operation. 